IPC: Add attachment brokering support to the message header.

ipc/brokerable_attachment.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef IPC_BROKERABLE_ATTACHMENT_H_
 #define IPC_BROKERABLE_ATTACHMENT_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
 #include "ipc/ipc_export.h"
 #include "ipc/ipc_message_attachment.h"
 
 namespace IPC {
 
 // This subclass of MessageAttachment requires an AttachmentBroker to be
 // attached to a Chrome IPC message.
 class IPC_EXPORT BrokerableAttachment : public MessageAttachment {
  public:
   static const size_t kNonceSize = 16;
   // An id uniquely identifies an attachment sent via a broker.
   struct IPC_EXPORT AttachmentId {
     uint8_t nonce[kNonceSize];
 
+    // Default constructor returns a random nonce.
+    AttachmentId();
+
+    // Constructs an AttachmentId from a buffer.
+    AttachmentId(const char* start_address, size_t size);
+
+    // Writes the nonce into a buffer.
+    void SerializeToBuffer(char* start_address, size_t size);
+
     bool operator==(const AttachmentId& rhs) const {
       for (size_t i = 0; i < kNonceSize; ++i) {
         if (nonce[i] != rhs.nonce[i])
           return false;
       }
       return true;
     }
 
     bool operator<(const AttachmentId& rhs) const {
       for (size_t i = 0; i < kNonceSize; ++i) {
         if (nonce[i] < rhs.nonce[i])
           return true;
         if (nonce[i] > rhs.nonce[i])
           return false;
       }
       return false;
     }
   };
 
   enum BrokerableType {
+    PLACEHOLDER,
     WIN_HANDLE,
   };
 
   // The identifier is unique across all Chrome processes.
   AttachmentId GetIdentifier() const;
 
   // Whether the attachment still needs information from the broker before it
   // can be used.
   bool NeedsBrokering() const;
 
-  // Fills in the data of this instance with the data from |attachment|.
-  // This instance must require brokering, |attachment| must be brokered, and
-  // both instances must have the same identifier.
-  virtual void PopulateWithAttachment(
-      const BrokerableAttachment* attachment) = 0;
-
   // Returns TYPE_BROKERABLE_ATTACHMENT
   Type GetType() const override;
 
   virtual BrokerableType GetBrokerableType() const = 0;
 
+// MessageAttachment override.
+#if defined(OS_POSIX)
+  base::PlatformFile TakePlatformFile() override;
+#endif  // OS_POSIX
+
  protected:
   BrokerableAttachment();
-  BrokerableAttachment(const AttachmentId& id, bool needs_brokering);
+  BrokerableAttachment(const AttachmentId& id);
   ~BrokerableAttachment() override;
 
-  void SetNeedsBrokering(bool needs_brokering);
-
  private:
   // This member uniquely identifies a BrokerableAttachment across all Chrome
   // processes.
   const AttachmentId id_;
 
-  // Whether the attachment still needs to be filled in by an AttachmentBroker.
-  bool needs_brokering_;
   DISALLOW_COPY_AND_ASSIGN(BrokerableAttachment);
 };
 
 }  // namespace IPC
 
 #endif  // IPC_BROKERABLE_ATTACHMENT_H_